1. Field of the Invention
The invention relates to a hot-rolled sheet steel especially useful for deep drawing, said sheet preferably being produced on a strip mill.
2. Discussion of the Background
The forming properties of steels are important in the production of deep-drawn articles having complex shapes. Among the available types of hot-rolled sheets or plates with mechanical properties obtained by controlled rolling on a wide strip rolling mill, the steels having the best deep-drawing properties are those designated as "3C" and "3C Ti".
These steels have in their compositions carbon, manganese, titanium, and certain trace elements which contribute to the desired mechanical properties. Their content of gamma-genic elements (e.g. carbon and manganese) is so high that their ferritic transformation temperature is relatively low; e.g. the AR3 transformation temperature is 840.degree. C. at a thickness of 4.5 mm. In order to avoid rolling in the biphase austenitic-ferritic domain, which would result in markedly inferior forming properties, the rolling temperature must be above 840.degree. C., i.e. must be in the austenitic domain.
In practice, a sheet comprised of these steels may be subjected to continuous coating on a galvanization line, to provide corrosion protection. This coating method tends to subject the sheet to a thermal cycle which results in an increase in the elastic limit of the steel and a reduction in its elongation at fracture.